1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head used for thermally-assisted magnetic recording in which a magnetic recording medium is irradiated with near-field light beam, thereby anisotropic magnetic field of the medium is lowered, thus data can be written. Further, the present invention relates to a head gimbal assembly (HGA) provided with a suspension for supporting the thermally-assisted magnetic recording head, and to a magnetic recording apparatus provided with the HGA.
2. Description of the Related Art
As the recording density of a magnetic recording apparatus, as represented by a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. Particularly, in the magnetic recording medium, it is necessary to decrease the size of magnetic micro particles that constitute the magnetic recording layer of the medium, and to reduce irregularity in the boundary of record bit in order to improve the recording density. However, the decrease in size of the magnetic micro particles raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume. As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy Ku of the magnetic micro particles. However, the increase in energy Ku causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. As a result, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the upper write field limit.
Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording technique was proposed. In the technique, a magnetic recording medium formed of a magnetic material with a large magnetic anisotropy energy Ku is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion, just after that, writing is performed by applying write magnetic field to the heated portion.
In the thermally-assisted magnetic recording, a technique is well known, which utilizes a near-field optical device as a metal piece that generates near-field light from plasmon excited by irradiated laser light. For example, U.S. Pat. No. 6,768,556 and U.S. Pat. No. 6,649,894 disclose a technique in which near-field light is generated by irradiating a metal scatterer with light and by matching the frequency of the light with the resonant frequency of plasmon excited in the metal.
As described above, various kinds of thermally-assisted magnetic recording systems with near-field optical devices have been proposed. Meanwhile, the present inventors have devised a near-field optical device in which laser light is coupled with the near-field optical device in a surface plasmon mode to cause excited surface plasmon to propagate to the opposed-to-medium surface, thereby providing near-field light, instead of directly applying laser light to a near-field optical device. The near-field optical device is hereinafter referred to as a surface plasmon generator. In the surface plasmon generator, its temperature does not excessively rise because laser light is not directly applied to the surface plasmon generator. As a result, there can be avoided a situation in which the end of a read head element, which reaches the opposed-to-medium surface, becomes relatively far apart from the magnetic recording medium due to the thermal expansion of the near-field optical device, which makes it difficult to properly read servo signals. In addition, there can also be avoided a situation in which the light use efficiency of a near-field light generating optical system including a near-field optical device is degraded because thermal fluctuation of free electrons increases in the near-field light generator.
Here, the near-field light generating optical system is an optical system that includes a waveguide and a near-field optical device, and the light use efficiency of the near-field light generating optical system is given by IOUT/IIN(×100), where IIN is the intensity of laser light incident to the waveguide, and IOUT is the intensity of near-field light emitted from a near-field light generating end of the near-field optical device after converting the laser light into surface plasmon in the near-field optical device.
When performing thermal-assisted magnetic recording in practice by using the above-described near-field light generating optical system including the surface plasmon generator, if the end surface of the surface plasmon generator departs from the end surface of the magnetic pole in the opposed-to-medium surface, the write ability will be extremely decreased because a long distance between the heat source and the magnetizing source. Contrary to this, if the end surface of the surface plasmon generator closes to the end surface of the magnetic pole, it is difficult to efficiently heat the magnetic medium because the generated plasmon will strongly affected by the magnetic pole.